1. Field of the Invention
The present invention relates to the production of separable slide fasteners, and more particularly to a method of and an apparatus for applying reinforcing film pieces of thermoplastic synthetic resin to a slide fastener chain at its longitudinally spaced element-free or blank tape portions.
2. Prior Art
U.S. Pat. No. 4,299,027, issued Nov. 10, 1981, discloses an apparatus for applying reinforcing film pieces of thermoplastic synthetic resin to a pair of unengaged slide fastener stringers at their longitudinally spaced element-free or blank tape portions. In the prior apparatus, a reinforcing film piece is fused completely to the blank tape portions of an adjacent pair by a shaping die and a coacting ultrasonic horn at a single station. The prior apparatus is not suitable for use in production of separable slide fasteners each having a separable bottom end stop; in that production, a pair of pin-like members to which a pin and a box of the separable bottom end stop are to be attached, must be formed on the blank tape portions of an adjacent pair along their inner edges, requiring a relatively high operating temperature of the ultrasonic horn. This high temperature impairs not only the reinforcing film piece but also the stringer tapes. With this arrangement a sufficient quality of slide fastener chain, for production of separable slide fasteners, cannot be obtained.